how do I calculate a pumps psi output?


by jimhebert
Tags: output, pumps
jimhebert
jimhebert is offline
#1
Mar9-12, 11:37 AM
P: 29
I have a pump that puts out 396 gal/hr of water. The output pipe on the pump is 9/16 inch in diameter. Is there a way to calculate the psi?
Phys.Org News Partner Physics news on Phys.org
Physicists consider implications of recent revelations about the universe's first light
Vacuum ultraviolet lamp of the future created in Japan
Grasp of SQUIDs dynamics facilitates eavesdropping
russ_watters
russ_watters is offline
#2
Mar9-12, 11:48 AM
Mentor
P: 22,007
It can be done but it isn't easy: you have to add up the pressure losses of all of the components of the piping system
jimhebert
jimhebert is offline
#3
Mar9-12, 12:15 PM
P: 29
Ok, I thought maybe there was a simple formula that could be applied. Thank You anyway.

On second thought, the piping is the same size as the outlet and it is only about 6 feet long, but the pump will be pumping the water up. It's for an aquarium.

256bits
256bits is offline
#4
Mar9-12, 05:10 PM
P: 1,271

how do I calculate a pumps psi output?


Quote Quote by jimhebert View Post
I have a pump that puts out 396 gal/hr of water. The output pipe on the pump is 9/16 inch in diameter. Is there a way to calculate the psi?
Pumps have a charcteristic that they will produce a certain flowrate at a certain head. I assume you mean 396 gal/hr at zero head. As the head is increased by adding more pipe to the pump exit, the flowrate decreases, up to a point where there will be a maximum pressure at the pump but no flow. By plotting several points on a graph of flow versus head, one obtains a pump characteristic curve.

The system curveon the other hand of all the losses in the pipe is more difficult to obtain as Russ mentioned.

The intersection of the system curve with the pump characteristic curve will give you the point at which the pump is operating.

On second thought, the piping is the same size as the outlet and it is only about 6 feet long, but the pump will be pumping the water up. It's for an aquarium.
The 6 foot pipe section upwards will give only the elevation head loss for the system curve.
jimhebert
jimhebert is offline
#5
Mar9-12, 05:17 PM
P: 29
The 396 gall/hr is the flow rate with the 6 feet of head according to the chart that you are mentioning. So I guess it is still not possible to calculate the psi?
Hassan2
Hassan2 is offline
#6
Mar10-12, 12:07 AM
P: 404
We can roughly approximate the head if we know the pump input power and the efficiency.

The efficiency of pumps are usually between 60% and 70% and of the driver ( motor) is above 90%.

The output power of the the pump is the flow rate times head.

If the driver is running with for example 50 W, for the flow rate of 396 gal/hr ( about 0.0004 m3/sec), we will get

[itex]\Delta P=\frac{50\times 0.65 \times 0.9}{0.0004}=0.7 KPa[/itex]

which is about 7 meters of water .
jimhebert
jimhebert is offline
#7
Mar10-12, 03:29 AM
P: 29
These specs may help in your calculations. The pump is a 3.5 horsepower.

The watts are 68, voltage =120, amps=.7
The Q max GPH = 687 gph
The Q min GPH = 449 gph
Head max =12.5 feet
Hassan2
Hassan2 is offline
#8
Mar10-12, 04:01 AM
P: 404
Quote Quote by jimhebert View Post
These specs may help in your calculations. The pump is a 3.5 horsepower.

The watts are 68, voltage =120, amps=.7
The Q max GPH = 687 gph
The Q min GPH = 449 gph
Head max =12.5 feet
The pump horsepower seems too much! According to your number, your pump can do more work as 3 horses can do. Such a pump needs a powerful driver not a 68 watt one.
jimhebert
jimhebert is offline
#9
Mar10-12, 04:12 AM
P: 29
You mean it is not a 3.5 HP pump as the specifications say? According to your calculations, you believe it to be a 3 HP....Correct?
Hassan2
Hassan2 is offline
#10
Mar10-12, 04:26 AM
P: 404
Quote Quote by jimhebert View Post
You mean it is not a 3.5 HP pump as the specifications say? According to your calculations, you believe it to be a 3 HP....Correct?
I expected a much less hp. Something like 0.1 HP. Or perhaps its 3/5 hp rather than 3.5 hp.

See this online calculator http://www.engineeringtoolbox.com/pu...wer-d_505.html
jimhebert
jimhebert is offline
#11
Mar10-12, 06:21 AM
P: 29
In the calculator I entered q=687, and h=12.15 and shaft bph =3.52
Hassan2
Hassan2 is offline
#12
Mar10-12, 06:45 AM
P: 404
Quote Quote by jimhebert View Post
In the calculator I entered q=687, and h=12.15 and shaft bph =3.52

The calculator gets the flow in units of gallon/minute. Yours is per gallon/hour
jimhebert
jimhebert is offline
#13
Mar10-12, 07:17 AM
P: 29
I didn't notice that. This is a web page that says 3.5 HP and I also have the actual pump.

http://www.petsuppliesnow.com/produc...UMP-660GP.html


I'll call the company to find out what is going on.
jim hardy
jim hardy is offline
#14
Mar10-12, 08:53 AM
Sci Advisor
jim hardy's Avatar
P: 3,147
That's a picture of an aquarium pump not a lawn sprinkler pump.
That much power would wreck an aquarium.
HP must mean something else. Probably "High Performance".

Figure the power it takes to lift the weight of 687 gallons of water twelve and a half feet in an hour.
F X D / T .
(8.3 X 687) X 12.5 / 3600 = 19.8 ft-lbs/sec = .036 hp by my back of envelope, ~26 watts.



To OP's question about discharge pressure - it's given in your spec.
Centrifugal Pump "head" is the discharge pressure given in units " height of fluid flowing."
Convert 12.5 feet of water to PSI.
Were the pump instead pumping mercury, its discharge would be 12.5 feet of mercury and input power would be much higher.
jim hardy
jim hardy is offline
#15
Mar10-12, 09:12 AM
Sci Advisor
jim hardy's Avatar
P: 3,147
Found its discharge curve..

http://www.f3images.com/IMD/MD_image...cra_Silent.jpg



i'd say 3.5 meters is about all the useful lift you'll get.

Credit is due this online store for posting the information. I like an outfit with that attention to detail.

http://www.marinedepot.com/ps_viewit...content=XJ1141
jimhebert
jimhebert is offline
#16
Mar10-12, 01:08 PM
P: 29
I bought this pump in pet shop and they had one in use in an aquarium. I do want to use it in a large tank. I would still like to know the approximate PSI output curve if possible.

The posted curve is not plotted correctly. The column with all the Syncras needs to be lifted up 2 increments and the H/m shifted to the right.
Hassan2
Hassan2 is offline
#17
Mar10-12, 01:19 PM
P: 404
Quote Quote by jimhebert View Post
I bought this pump in pet shop and they had one in use in an aquarium. I do want to use it in a large tank. I would still like to know the approximate PSI output curve if possible.

The posted curve is not plotted correctly. The column with all the Syncras needs to be lifted up 2 increments and the H/m shifted to the right.
The plot seems fine. The column of Syncras is there just tell you ,by color , that which curve is for which pump. It has nothing with the vertical axis.

3.5 meters is not enough for your purpose? by the way, isn't pressure in unit of meters/ft of water easier to understand? I wonder why you keep asking the psi.
jimhebert
jimhebert is offline
#18
Mar10-12, 01:54 PM
P: 29
I want to attach another device to the pump and it requires a certain psi to function properly.


Register to reply

Related Discussions
Calculate useful energy output...? Classical Physics 1
Calculate Dynamo Max Power Output Classical Physics 2
How to calculate output of a motor used as a generator Electrical Engineering 4
How to calculate NPIPA & NPIPR for PD pumps Mechanical Engineering 2